Shrink sleeves are widely used to form water-proof connections have electrical and other cables, especially at cable connections, branches or the like, wherein the sleeve or sheath of a thermally shrinkable thermoplastic synthetic resin is slipped over the cable across the connection or branch and is then heated to shrink the sleeve around the cable insulation on either side of the junction and around the conductors connected at this junction.
At the ends of this sleeve, the latter hugs the insulation and can form a water-proof and hermetic seal thereagainst, the seal bridging the connection so that the entire joint is sealed satisfactorily against the incursion of moisture and against electrical leakage.
Shrink sleeves of the type described have been internally coated with an adhesive which allows a sufficient adhesion with the cable to be achieved. Conventional adhesives for this purpose, however, have failed when pressurized cable networks are employed, i.e. the monitoring of the cable network is effected through the gas (e.g. compressed air) pressurization of the conductors within the insulation jacket thereof. In these cases, the adhesive may lose its effectiveness because of the internal pressure, especially over long periods of time and with use of the cables in elevated temperature environments, thereby causing the shrink sleeve to lose its effectiveness.
While special adhesives have been developed for use in conjunction with pressurized gas monitoring of the integrity of cable networks, these adhesives contribute to a significantly thicker and therefore harder and less flexible sleeve and require, for example, fiber-reinforced sleeves as are described in DE 38 33 415 and EP 0 116 393.
For standard shrink sleeves with a thickness, for example, of about one half those of the special sleeves mentioned above, an adhesive has been provided which has a fifty times greater viscosity than conventional melt adhesives and which satisfies the requirements in pressurized systems. However it has been found that such adhesives require an increased supply of heating to make them effective so that during installation thermal deterioration of the shrink sleeve can occur.
Additionally, it has been found to be a drawback with shrink sleeves that the application of especially high temperatures can give rise to a combustion of the sleeve materials and can spread fire from droplets of the adhesive or combustion of the deteriorating sleeve, thereby reducing the adhesion of the sleeve and its sealing effectiveness and contributing to the spread of fire.
Indeed, as a rule the viscosity of an adhesive will drop with increased heating so that especially at the ends of the sleeve droplets of the adhesive can emerge to present the danger of combustion and fire spread.
As increasing temperature, the stresses within the sleeve can increase to the point that the sleeve can tear and on occasion can completely fall off from the cable splice and/or the cable. There is thus a significant danger even with partial heating of tearing of the sleeve and melting of the adhesive to the point that droplets thereof may emerge in a detrimental manner.